Question

During osmosis, flow of water through a semi-permeable membrane is:
A. From both sides of semi-permeable membrane with equal flow rates
B. From both sides of semi-permeable membrane with unequal flow rates
C. From solution having lower concentration only
D. From solution having higher concentration only

Answer 1

Hint:
Understanding of what osmotic pressure is and how it will affect the flow of solvent can be used to find out the direction of flow.

Complete step by step solution
We know that a semi-permeable membrane is one that only allows smaller particles to flow through it but not to that of a bigger one. In a solution, it is usually the flow of solvent whereas solute particles are kept blocked on one side of the membrane in solution only.

Now, as per our understanding of lowering in vapor pressure of a solvent upon addition of a solute leads to a difference between the pressure on the solvent side of the membrane and on the solution side. Solvent has a high vapor pressure being pure whereas it is lower for solution. This results in flow of solvent from high pressure to lower which is known as osmosis. A pressure can be applied just to stop this flow and it is known as osmotic pressure of the solution.

In terms of concentration, we can say that the solvent flows from lower to higher concentration. The same is true when our solvent is water and we can observe this in the case of shriveling of raw mangoes when they are put in salt water. Concentration is higher in the salt water so water flows from inside of mangoes to outside making them shriveled.

In addition to the above understanding of flow of water we also have to consider that it is net flow of water that resulted from unequal flow rates of water on the two sides of the semi-permeable membrane.

Hence, the correct option is B.

Note:
We have to keep in mind that in lower concentration, we have only pure solvent (high vapor pressure as there is no solute) whereas in higher concentration, pressure is low because solute particles are present.